When the loan is going through escrow, it is the escrow officers job to make sure that there are not any liens against the home. I handle the finance side and when my clients come to me and ask this question we are able to talk with title/escrow and do a lien search. That part anyways does not fall on you. The lender you are using wont allow the loan to record without clear title anyways. If you have any other questions dont hesitate to contact me.
Title companies are the most helpful in this case you do have to request for a property profile and ask if they can check for any liens recorded. If you are interested in any homes on the MLS these are REO, Short Sale or traditional sales once open escrow the title company will run a title report and make sure is free and clear to close escrow.
Any title company can run a 'property profie' (generally free) if you provide a parcel number or street address although without paying for a preliminary title search the free report may not catch everything of record. You can also use the Clark County recorder's website.